One of these days, I'm going to write up a blog post on the dollars and cents of the solar on my roof. For now, at least, the short form is that buying a solar installation looks financially a lot like buying a 20 year bond. You pay money up front and it pays out monthly. What's unusual, versus bonds, is that the monthly payments are indexed with the price of electricity. If retail electricity becomes more expensive, then the yield from your panels (in dollars) goes up.

Translation: solar panels are something of a hedge against energy cost inflation. You shouldn't think of them as a cost item, but rather as an investment (of sorts). Of course, they're an investment that's literally tied to your house, so the only way you can liquidate the investment is to sell your house.

The trick to this investment is that you need to either have a way of selling your power back, or of storing it if you don't use it. You can buy a battery storage system, but that takes that expensive solar system and makes it yet again more expensive. I suspect that you'd only ever seriously pursue battery storage if you lived off-grid, or if you had one of these cool Japanese things where you can store power in your electric car battery and then draw it back out again. And that assumes you don't actually, you know, what to drive off in the morning with a full battery...